The present invention relates to processes of making cabazitaxel and intermediates thereof. Jevtana® is an injectable antineoplastic medicine whose active pharmaceutical ingredient (API), cabazitaxel, belongs to the taxane class and is closely related in both chemical structure and mode of action to the anticancer drugs paclitaxel (Taxol®) and docetaxel (Taxotere®). Cabazitaxel is prepared by semi-synthesis from 10-deacetylbaccatin III (10-DAB) which is extracted from yew tree needles. The chemical name of cabazitaxel is (2α,5β,7β,10β,13α)-4-acetoxy-13-({(2R,3S)-3-[(tert-butoxycarbonyl)amino]-2-hydroxy-3-phenylpropanoyl}oxy)-1-hydroxy-7,10-dimethoxy-9-oxo-5,20-epoxy-tax-11-en-2-yl benzoate and is marketed as a 1:1 acetone solvate (propan-2-one), having Formula A shown below. The acetone solvate of cabazitaxel is a white to off-white powder with a molecular formula of C45H57NO14.C3H6O and a molecular weight of 894.01 grams/mole for the acetone solvate and 835.93 grams/mole for the solvent-free form.

Cabazitaxel (also called dimethoxy docetaxel) is a dimethyl derivative of docetaxel, which itself is semi-synthetic, and was originally developed by Rhone-Poulenc Rorer and was approved by the U.S. Food and Drug Administration (FDA) for the treatment of hormone-refractory prostate cancer on Jun. 17, 2010. Cabazitaxel is a microtubule inhibitor. The acetone solvate crystalline form of cabazitaxel and a process for its preparation is disclosed in the U.S. Pat. No. 7,241,907.
U.S. Pat. No. 5,847,170 describes cabazitaxel and its preparation methods. One of the methods described in U.S. Pat. No. 5,847,170 includes a step-wise methylation of 10-DAB (the step-wise methylation method is shown in FIG. 1) to provide the key intermediate (2αR,4S,4αS,6R,9S,11S,12S,12αR,12βS)-12β-acetoxy-9,11-dihydroxy-4,6-dimethoxy-4α,8,13,13-tetramethyl-5-oxo-2α,3,4,4α,5,6,9,10,11,12,12α,12β-dodecahydro-1H-7,11-methanocyclodeca[3,4]benzo[1,2-b]oxet-12-yl benzoate, herein referred to as 7,10-di-O-methyl-10-DAB (XVa). The intermediate XVa is coupled with the 3-phenylisoserine side chain derivative VI to provide XVa′, which is followed by removal of the oxazolidine protecting group from the side chain of XVa′ to give cabazitaxel.
Another method described in U.S. Pat. No. 5,847,170 utilizes methylthiomethyl (MTM) ethers as shown in FIG. 2. MTM ethers can be prepared from alcohols using two common methods. One method comprises deprotonation of an alcohol with a strong base to form an alkoxide followed by alkylation of the alkoxide with a methylthiomethyl halide. This approach is only useful when the alcohol is stable to treatment with a strong base. 10-DAB and some of its derivatives in which C7-OH is not protected displays so instability in the presence of strong bases and epimerization of the C7-OH can occur upon contact of 10-DAB and some of its derivatives in which C7-OH is not protected with strong bases. Another method for the synthesis of MTM ethers from alcohols utilizes Ac2O and DMSO. One disadvantage of this method is that it can also lead to the oxidation of alcohols to aldehydes or ketones. For example when the synthesis of the 10-di-O-MTM derivative of 10-DAB without protecting groups at the C13 hydroxyl group is attempted undesired oxidation of the C13-OH to its corresponding ketone occurs.
U.S. Pat. No. 5,962,705 discloses a method for dialkylation of 10-DAB and its derivatives to furnish 7,10-di-O-alkyl derivatives, as shown in FIG. 3. This has been demonstrated as a one-step, one-pot reaction, however, provides the best isolated yield when potassium hydride is used at −30° C. From an industrial point of view, the use of low reaction temperature is less favorable than using ambient temperature. Furthermore the use of a strong base can cause some epimerization of the C7-OH chiral center with an associated loss of yield. Potassium hydride is a very reactive base and must be treated with great caution.
Accordingly, there is a need for an alternative processes for the preparation of cabazitaxel and its key intermediate, 7,10-di-O-methyl-10-DAB (XVa) that is short in number of synthetic steps and avoids the use of low temperatures and strong bases such as metal hydrides in the C7-O methyl ether formation step. Such a process would also be useful for the preparation of analogues of cabazitaxel wherein the C7-O and C10-O functional groups were substituted with other alkyl groups.